Gum arabic is a natural exudate from the trunks and branches of the plants that belong to the genus Acacia (especially, Acacia senegal and Acacia seyal) of the Leguminasae family. Gum arabic is highly soluble in water and its aqueous solution provides high emulsifiability, emulsion stability, encapsulation ability, adhesiveness, protective colloid property and filmforming ability even at low concentration, so that it has been widely used as an emulsifier, thickener, stabilizer, binder, and coating agent.
Gum arabic is collected in various countries in the Sahara region of Africa and has a wide variation in molecular weight and composition of constituent components due to differences in the soil and climate in each habitat and age of the original tree. For this reason, functions of gum arabic in its original state delivered from the habitat are nonuniformity, and thereby properties of preparation using the gum arabic are not consistent (Williams, P. A. and Phillips, G. O., (2000) in Handbook of Hydrocolloids, pp. 155-168, Editors: Williams, P. A. and Phillips, G. O., Woodhead, London and New York). In the present specification, such gum arabic is referred to as simply “gum arabic” or “natural gum arabic” or “unmodified gum arabic”, as distinguished from “modified gum arabic” of the present invention.
As mentioned above, emulsifiability is one of the useful properties that gum arabic exhibits in a wide variety of products. Several methods have been proposed and studied to reduce as much as possible the variation of emulsifiability between samples attributable to the variation of the properties of natural gum arabic and to enhance emulsifiability. For instance, one method comprises removing metal ions from gum arabic to obtain arabic acid and subjecting it to thermal modification to improve its emulsifiability (Japanese Unexamined Patent Publication No. 1990-49001), and another method comprises modifying gum arabic having a loss-on-drying of not more than 50 weight % by heating it at 60-140° C. for not less than 30 minutes to thereby enhance its emulsifiability (Japanese Unexamined Patent Publication No. 2000-166489).
However, these methods do not satisfactorily modify gum arabic so as to obtain the expected emulsifiability. Therefore, effective methods for manufacturing a modifying gum arabic having uniform quality and improved emulsifiability are still required. Furthermore, it is necessary to develop a method for manufacturing modified gum arabic, which has improved properties, such as emulsion stability, encapsulation ability, adhesiveness, protective colloid property, or filmforming ability, as well as the above-mentioned emulsifiability, and has a uniform quality by being reduced variation between natural gum arabic samples.
Documents relating to gum arabic include the following Documents 1-4 can be listed, in addition to the aforesaid documents.    Document 1: Mikio Nakamura, Pharmaceutics, Vol. 42, No. 1 (1982) pp. 25-29.    Document 2: Carbohydrate Research, 246 (1993) pp. 303-318    Document 3: WO02/072862    Document 4: Japanese Unexamined Patent Publication No. 1983-18370